Photosynthesis: How Plants Make Food

Photosynthesis: How Plants Make Food

• Plants create their own sustenance through a process known as photosynthesis.
• "Photo" signifies light, while "synthesis" denotes creation, thus photosynthesis equates to "making with light."
• Photosynthesis involves plants utilizing water from the soil, carbon dioxide from the air, and energy from sunlight.
• Chlorophyll, a green pigment within plant cells, captures sunlight.
• This captured energy drives a chemical reaction combining water and carbon dioxide.
• The reaction yields glucose and oxygen.
• Photosynthesis can be summarized by the equation: water + carbon dioxide → glucose + oxygen.
• Photosynthesis predominantly occurs in plant leaves.

Experiment: Collecting Gas Produced During Photosynthesis

• This experiment employs a water plant to easily gather released gas.
• Submerge a water plant in a beaker filled with pond or tap water.
• Position the apparatus in sunlight for at least a day.
• Collect the gas that accumulates in the test tube.
• Carefully remove the tube, ensuring the opening stays under water to prevent gas escape.
• Seal the tube with a stopper and position it upright in a rack.
• Test the gas with a glowing splint; oxygen presence will cause the splint to relight.
• Water plants are ideal due to their aquatic nature, which simplifies gas collection.
• Sunlight is essential as it fuels the process of photosynthesis.

Experiment: Investigating Light Intensity's Effect on Photosynthesis

• This experiment determines how varying light amounts affect bubble production in water plants.
• Set up the equipment with a lamp near the test tube.
• Allow approximately 5 minutes for the plant to adapt and commence photosynthesis.
• Measure the distance between the lamp and test tube.
• Count and record the number of bubbles produced per minute.
• Repeat bubble counts multiple times at each distance
• Vary the lamp's distance and repeat measurements.
• Calculate the average bubble count for each distance.
• Create a graph plotting lamp distance on the x-axis and mean bubble count on the y-axis.
• As the lamp's distance increases, light intensity decreases.
• Higher light intensity leads to an increased rate of photosynthesis.

Importance of Photosynthesis

• It provides energy in the form of nutrients for other organisms.
• Plants convert sunlight into glucose and other carbohydrates, storing energy.
• Animals obtain energy by consuming plants, thus transferring the plant-captured energy.
• It provides oxygen to Earth's atmosphere, essential for plant and animal respiration.
• Approximately 20% of the air is composed of oxygen, a byproduct of photosynthesis.
• Initially, Earth's atmosphere was nearly devoid of oxygen.
• Photosynthetic bacteria initiated oxygen accumulation.
• No animals would exist if photosynthesis had not developed.

Photosynthesis Details

• Chlorophyll, capturing sunlight energy and enabling the reaction between water and carbon dioxide, is vital.
• Chlorophyll resides within chloroplasts inside plant cells, making chloroplasts the site of photosynthesis, not all plant cells contain chloroplasts.
• Leaf cells in most plants contain numerous chloroplasts.
• Plants transform carbon dioxide and water into carbohydrates and oxygen within leaf cells.
• Excess carbohydrates are stored as starch for later use, particularly during low sunlight conditions.
• Testing for starch confirms if a leaf has undergone photosynthesis.

Experiment: Testing a Leaf for Starch

• Utilize the iodine test to determine if a leaf has undergone photosynthesis.
• Boil the leaf in water to rupture cell membranes.
• Decolorize the leaf in ethanol to eliminate chlorophyll.
• Spread iodine solution; a blue-black color indicates starch presence.
• Starch is located in chloroplasts.
• Boiling is required to permeate cell membranes for the test.
• Decolorization enhances visibility of the iodine reaction.
• Starch in the leaf implies photosynthesis.
• Green parts of the leaf contain starch, confirming the presence of chlorophyll/photosynthesis.

Inside a Leaf

• Photosynthesis takes place in chloroplasts within leaf cells.
• Chloroplasts are primarily concentrated in the middle layers of leaves.
• Leaves' thin structure facilitates sunlight penetration to cells.
• Leaves need water and carbon dioxide for photosynthesis.
• Water reaches cells via veins.
• Stomata, tiny holes in leaves, facilitate gas exchange.
• Air spaces between cells aid in gas diffusion.
• The upper epidermis is the surface layer on the leaf, and stops water from evaporating.
• The palisade layer contains cells that do the most photosynthesis.
• The spongy layer does a small amount of photosynthesis

Minerals and Plant Growth

• Fertilizers enrich crops by supplying essential minerals.
• Plants require minerals from the soil in moderate amounts.
• Magnesium and nitrate are key minerals.
• Magnesium is essential for chlorophyll production; deficiency causes yellow leaves and stunted growth.
• Nitrate, containing nitrogen, aids in converting carbohydrates into proteins for cell production and growth; deficiency results in small size and leaf death.
• Nitrogen is also needed to make chlorophyll.
• Farmers assess soil mineral content to guide fertilizer use.
• GPS technology enables precise fertilizer application.

Carbon in Living Organisms

• Carbon is an element (symbol C) crucial for life.
• Organisms use carbon as part of a compound.
• Carbon is present in carbohydrates, proteins, and fats.
• Plants acquire carbon dioxide from the atmosphere and convert it into carbohydrates via photosynthesis.
• Plants create proteins and fats from carbohydrates, all containing carbon atoms.
• Animals obtain carbon by consuming plants or other animals.
• Decomposers secure carbon by breaking down plant and animal waste.
• Carbon moves through food chains, illustrating energy and carbon atom transfer.
• The human body comprises carbon-containing compounds.

Carbon Dioxide Return to the Air

• Carbon dioxide is reintroduced into the atmosphere when organisms respire.
• Organisms respire, including plants, releasing carbon dioxide, all the time.
• .Decomposers release carbon dioxide as they break down waste.

Fossil Fuels and Combustion

• Decomposers may not break down dead organisms fast enough, that creates sediment that leads to fossil fuels.
• Fossil fuels take a long time to form.
• Oil and gas formation occurs through marine organism remains.
• Coal originates from plant remains.
• Fossil fuels contain carbon, which turns into carbon dioxide when burned (combustion).
• The combustion process combined with the carbon cycle represents the full cycle of carbon in environemnt.
• Carbon is released back into the air upon burning fossil fuels.
• Rising carbon dioxide levels impact Earth's climate.

Climate Change

• Climate is long term patterns of rainfall and temperature.
• The Earth's climate has varied over time.
• Ice Ages: Earth has experienced warm and cold cycles, where ice was/was not present at the poles.
• Snowball Earth: Roughly 650 million years ago, the Earth was covered in ice and snow.
• Asteroid Collisions: Asteroids colliding can release debris that blcoks light and heat from the sun, which causes ice ages. An example of this is the asteroid that hit earth 67 million years ago, which led to planet-wide devastation.

Current Climate Change

• Current climate has been significantly stable for 2000 years.
• Mean temperatures are rising because of carbon dioxide concentration.
• Rising average temperatures can disrupt climate patterns.

Impact of Climate Change

• Extreme weather events: increased energy in the atmosphere causes hurricanes and typhoons.
• Unpredictable rainfall: the timing of rainfall can change.
• Rising sea levels: water expands because of higher temperatures, and the melting of ice contributes to rising sea levels. Sea levels rising is a threat to coastal cities.
• By he end of the century, seal level is predicted to rise 3mm per year.